I need carpentry help!!!

I need to build a 16' Wide cornice for the top of a window. I need it to be 24" High so I can use one sheet of ply, cut in two for the front. My big question is....How can I join the two 8' boards together, showing minimal seem? I am adding crown and painting it when finished, and need the front to look as seemless as possible when finished. I don't care what the back looks like as long as the front looks great. What are my best options? I'm thinking wood putty and sanding, will that work? Any suggestions would be greatly appreciated.

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A scarf joint would probably better than just butting the two pieces together. That's where the edges are beveled at 30-45 degrees so one overlaps the other. Wood glue and some nails would be a good idea as well.

Do an internet search for scarf joint and you'll see how it is often done for base moulding.

But 1/2" ply would be overkill as you don't need the strength. I would use 1/4" MDF that my local plywood supplier would rip down for me. To hold the two sections together I would buy an additional 1/4" sheet ripped in half and cut so that one piece is 8' long and the other piece is cut in half to get two 4' pieces.

1) Lay the two 8x2' sections on a very Flat surface, end to end.

2)Starting at either end, with titebond, glue one of the 4' sections to the back of the 8' section.

3) Then making sure that the two 8' sections are still tightly abutted glue down the remaining 8' section so that it bridges the connection point to hold the fascia together.

4) Finally glue down the last 4' section so that you end up with a laminate of two MDF supporting layers.

I vote for the scarf joint, with one suggestion. As these pieces will be 24" high x 16 ft. long and standing in a vertical position, it appears they will have to have some type of frame backing them. I would add some wood filler between the scarf joint AS I placed the two sheets together on the frame, allowing some filler to "ooze" out. When all of this is in place and the filler has dried, then a light sanding of all the wood, including the excess filler should make this seam virtually seamless. I'm picturing that with the crown and painting this will make a very nice cornice project. Good Luck, David

sheetrock instead of ply?

They make little flat plates that you can attach to each piece of wood on the back of cornice to hold seam together. Use small screws. Can get them at Lowes or other home improvement stores.They are flat pieces of metal with lots of holes in and are very strong. Good luck!